PCB Surface Finish Comparison

The surface finish is the thin protective coating on exposed copper pads that keeps them solderable and prevents oxidation. It looks like a minor line item on a fab quote, but the wrong choice shows up later as poor coplanarity, tombstoning, or short shelf life. Here is how the four common finishes compare.

The contenders

HASL (leaded) — hot air solder leveling with tin-lead. Cheap and forgiving, but uneven surface and RoHS-restricted.
Lead-free HASL — the RoHS-compliant version, slightly less coplanar and higher process temperature.
ENIG — electroless nickel / immersion gold. Flat, fine-pitch friendly, longer shelf life.
Hard gold — electroplated gold over nickel, built for wear on contacts and gold fingers.

Side by side

Finish	Flatness	Cost	Shelf life	Best for
HASL (leaded)	Poor	Lowest	~12 mo	Through-hole, coarse pitch
Lead-free HASL	Poor-fair	Low	~12 mo	RoHS, coarse pitch
ENIG	Excellent	Medium-high	~12 mo+	Fine-pitch BGA, HDI
Hard gold	Excellent	Highest	Very long	Edge contacts, ATE

Choosing

Flatness is the deciding factor for fine-pitch assembly: HASL's uneven bumps make 0.4 mm BGAs and QFNs unreliable, which is why ENIG dominates dense boards. Hard gold is reserved for surfaces that see mechanical wear — connector fingers and test-board contacts — because it is expensive and not ideal as a general solderable finish (thick gold can embrittle joints).

Engineering noteA common mistake: specifying hard gold on all pads to "improve quality." Thick gold dissolves into the solder joint and can embrittle it. Use ENIG for solderable pads and reserve hard gold for contact edges.

For most modern boards, ENIG is the safe default; HASL survives where cost rules and pitch is coarse; hard gold is a contact-wear solution, not a general finish.